Gastrointestinal disorders, including viral, bacterial and protozoal infections, as well as chronic inflammatory diseases, or radiation damages, exert a stress on gastrointestinal cells. The main nutrient of mucosal cells of the gastrointestinal tract is glutamine. This amino acid, usually non-essential, becomes "conditionally essential" in pathologies characterized by a glutamine requirement that exceeds the individual's ability to produce sufficient amount of this amino acid. Enteral or parenteral administration of glutamine improves nutritional management and recovery of the patients (Castel L M et al. (1994) Amino Acids 7, 231-243; Lacey J M, Wilmore D W (1990) Nutr. Rev. 48 (8), 297-309). Glutamine, apart from being the preferred fuel for cells with a rapid proliferation rate such as enterocytes and lymphocytes, is also a regulator for acid-base balance through the production of ammonia. Enterocytes are the most important cells of small intestine which use glutamine as an energy source (Wu G et al. (1995) Am. J. Physiol. 266, R334-R342; Nagy L E, Kretchmer N (1988) J. Nutr. 118 (2), 189-193). As a matter of fact, intestinal cells absorb a remarkable amount of glutamine supplied with the diet and whenever the supply of this amino acid is decreased, the amino acid is taken up from the blood. Low levels of glutamine, experimentally induced in animals, for instance through glutaminase administration, cause intestinal disorders, e.g. chronic diarrhoea, villous atrophy, etc., (Castel L M et al. (1994) Amino Acids 7, 231-243) thus confirming the importance of glutamine for the intestine. In conclusion, glutamine can be insufficient in certain disorders of the gastrointestinal tract. In such situations of glutamine deficiency, the gastrointestinal cells are more vulnerable and therefore more exposed to injury caused, for instance, by infectious agents or ionizing radiations. Conversely injury and stress to gastrointestinal cells can augment their energetic needs, and thus their requirement of glutamine for survival or replacement. Consequently glutamine administration can augment the ability of gastrointestinal cells to withstand injury. In addition, the above mentioned positive effects on gastrointestinal cells due to glutamine administration can be further enhanced by the addition of arginine which acts both on the immune system and the wound-healing rate (Wu G et al. (1995) Am. J. Physiol. 266, R334-R342). Carbohydrates are thought to act in synergy with glutamine, but alone they cannot substitute it (Wu G et al. (1995) Am. J. Physiol. 266, R334-R342).
In solution glutamine is not completely stable. In particular, during heat sterilization of glutamine solutions, pyroglutamate and glutamic acid may form. Glutamine containing polypeptides are much more stable. Upon ingestion of such polypeptides, glutamine may be released in the stomach and intestine by proteases. Therefore a sufficient amount of glutamine can be also achieved by administering small or large polypeptides containing glutamine such as for instance L-alanyl-L-glutamine or glycyl-L-glutamine or glycyl-glycyl-L-glutamine.
Lactic acid bacteria, particularly lactobacilli, as well as other bacteria isolated from the gastrointestinal tract of healthy human beings or animals, have long been known to produce a prophylactic and therapeutic effect on gastrointestinal infections (Zoppi G. et al.(1982) Eur. J. Pediatrics 139, 18-21). Such bacteria go under the name of eubiotic bacteria. Some bacterial species may compete with pathogenic ones for nutrients and/or attachment sites on the gastrointestinal mucous membrane. In addition they can favor the return of pH to normal values. For instance, the strain Enterococcus faecium SF 68 (earlier called Streptococcus faecium SF 68), originally isolated from pig intestines, has been proven to be effective in clinical studies (Borgia M et al. (1982) Curr. Ther. Res. 31(2), 265-271; Bellomo G et al. (1980) Curr. Ther. Res. 28(6), 927-936; Camarri E et al. (1981) Chemotherapy 27, 466-470; Wunderlich P F et al. (1989) J. Int. Med. Res. 17, 333-338). Due to a low affinity of this bacterium for the gastrointestinal mucous membrane, a regular administration for a prolonged period is needed. In contrast, patients treated with bacteria showing good adherence to the mucous membrane, will require less frequent and less prolonged administration to achieve a cure.
Bacteria belonging to the Lactobacills genus, which are able to adhere to human gastrointestinal mucous membranes, and thus competing with pathogens with similar adhering properties, have been isolated from healthy human beings and their characteristics are disclosed in U.S. Pat. No. 4,839,281, U.S. Pat. No. 5,032,399, and WO Patent Applications 95/33046. For instance, U.S. Pat. Nos. 4,839,281 and 5,032,399 disclose the Lactobacillus acidophilus strain ATCC 53103 isolated from adults and characterized by good adhesion properties. The taxonomic classification of the strain was more recently revised and the strain classified as Lactobacillus casei sbsp. rhamnosus. In certain countries dietary products based on this strain, commonly called Lactobacillus GG, have reached the market (e.g., Gefilus.sup.(R) fermented milk and Gefilus.sup.(R) fermented whey drink in Finland). Other strains, with dramatically improved adhesion properties, belonging to the genus Lactobacillus are the strains CNCM I-1390, CNCM I-1391, CNCM I-1392, and CNCM I-1447. They are disclosed in WO Patent Applications 95/33046. In addition to excellent adhesion properties they are characterized by favourable technological properties with respect to production and conservation.
Antibiotics are widely used to treat acute infections. The gastrointestinal flora become impoverished. Lactobacilli administration may be used to restore a well functioning flora. In such cases it could be useful to select bacteria which are resistant to antibiotics. As a matter of fact, many bacteria show an intrinsic resistance to antibiotics. Otherwise, antibiotic resistance can be induced by mutagenesis, for example by using agents which speed up the normal mutation rate. Then, the mutated strains are selected by well-known procedures. Alternatively, widely known techniques of genetic engineering can produce bacteria endowed with specific resistance to antibiotics.
Some eubiotic bacteria show a bacteriostatic or even bactericidal behavior toward pathogens. These activities partially result from the production of metabolites, such as lactic acid, acetic acid, and hydrogen peroxide, which make the environment less favorable for the growth of pathogens. In addition, several lactic acid bacteria are known to produce other substances such as antibiotics and bacteriocins. And obviously these bacteria gather special interest.